The Date for Monday and Friday of the current week can be determined as illustrated below.

SELECT GETDATE() + (2 - DATEPART(WEEKDAY, GETDATE())) AS MONDAY, GETDATE() + (6 - DATEPART(WEEKDAY, GETDATE())) AS FRIDAY

This assumes that you consider the first day of the week to be a Sunday and that the last day of the week is a Saturday.  If this is not the case you will need to use the SET DATEFIRST to set the first day of the week to a number from 1 through 7.  ie. SET DATEFIRST 1 to set MONDAY.  To determine the day that is currently set as the first day of the week run SELECT @@DATEFIRST (by default this is 7 which is Sunday).